Diaphragm and preparation method thereof, secondary battery and electric device

Abstract

The invention relates to a diaphragm and a preparation method thereof, a secondary battery and an electric device. The diaphragm comprises a first base film, a second base film and a middle layer arranged between the first base film and the second base film, the intermediate layer includes ceramic particles and polymer particles. The diaphragm has a sandwich composite structure, can prevent the middle layer from falling off, has good mechanical strength, can close pores under an overheating condition, and obviously reduces the thermal runaway probability of the battery under an abnormal high temperature condition.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a diaphragm and a preparation method thereof, a secondary battery and an electrical device. Background Art

[0002] In recent years, as the application scope of secondary batteries becomes wider and wider, secondary batteries are widely used in energy storage power supply systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0003] In the battery structure, the diaphragm is located between the positive electrode and the negative electrode, and is mainly used to separate the positive electrode and the negative electrode to prevent the two electrodes from short-circuiting due to contact. When a short circuit or other abnormality occurs in the battery, the temperature inside the battery cell rises sharply, causing the diaphragm to melt and easily cause thermal runaway. In the prior art, ceramic coatings are often used on the surface of the diaphragm to improve the thermal stability and mechanical strength of the diaphragm. However, there are still defects such as easy detachment of the ceramic layer and insufficient safety performance at abnormally high temperatures. Summary of the invention

[0004] The purpose of the present application is to provide a diaphragm and a preparation method thereof, a secondary battery and an electrical device. The diaphragm has a multi-layer composite structure, can avoid the shedding of the intermediate layer, has good mechanical strength, and can close the pores under overheating conditions, significantly reducing the probability of thermal runaway under abnormally high temperature conditions.

[0005] To this end, the first aspect of the present application provides a diaphragm, comprising a first base film, a second base film and an intermediate layer; the intermediate layer is arranged between the first base film and the second base film; the intermediate layer comprises ceramic particles and polymer particles.

[0006] By placing an intermediate layer including ceramic particles and polymer particles between two layers of diaphragms, a composite diaphragm with a sandwich structure is formed, which effectively avoids the problem of ceramic particles and polymer particles falling off easily. In addition, the diaphragm provided by the present application also has good mechanical strength and can close the pores under overheating conditions, significantly reducing the probability of thermal runaway under abnormally high temperature conditions.

[0007] In any embodiment, the porosity of the first base film is greater than the porosity of the second base film.

[0008] When two base membranes with different porosities are superimposed on each other, it is less likely that the fibers between them will clog the pores, which helps the membrane to have good air permeability; and it also helps to enhance the overall mechanical properties of the membrane.

[0009] In any embodiment, a ratio of the porosity of the first base film to the porosity of the second base film is greater than or equal to 1.02.

[0010] When there is a slight difference in the porosity of the first base film and the second base film, for example, when the ratio between the two is greater than 1.02, it can have a certain good technical effect in improving the overall air permeability of the diaphragm.

[0011] In any embodiment, the porosity of the first base film is 30% to 80%.

[0012] In any embodiment, the porosity of the second base film is 30% to 70%.

[0013] In any embodiment, the thickness of the first base film is greater than the thickness of the second base film.

[0014] When the porosity of the first base film is greater than that of the second base film, the thickness of the first base film is made greater than that of the second base film, so that the first base film with a relatively loose structure has a thicker thickness, which is beneficial to ensure that the diaphragm has good mechanical strength.

[0015] In any embodiment, a ratio of a thickness of the first base film to a thickness of the second base film is greater than or equal to 1.02.

[0016] In any embodiment, the thickness of the first base film is 1 to 12 μm; the thickness of the second base film is 1 to 12 μm.

[0017] In any embodiment, in the intermediate layer, the mass ratio of ceramic particles to polymer particles is 1.5-4.

[0018] In any embodiment, the average particle size Dv50 of the ceramic particles is 0.01 to 1 μm.

[0019] In any embodiment, the average particle size Dv50 of the polymer particles is 0.01 to 1 μm.

[0020] In any embodiment, the thickness of the intermediate layer is greater than or equal to 0.3 μm.

[0021] In any embodiment, the thickness of the intermediate layer is 0.5 to 5 μm.

[0022] In any embodiment, the material of the ceramic particles includes one or a combination of two or more of the following groups: boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium oxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), zirconium titanate (ZrTiO3), barium titanate (BaTiO3), and magnesium fluoride (MgF2).

[0023] In any embodiment, the melting point of the polymer particles is 200-260°C.

[0024] In any embodiment, the material of the polymer particles includes one or a combination of two or more of the following: polycaprolactam (nylon 6), polyhexamethylene adipamide (nylon 66), polydodecane diamide (nylon 612), polydecane diamide (nylon 1010), polydecene formamide (nylon 11), polydiphenyl ether sulfone, and polynonyl urea.

[0025] In any embodiment, the first base film and the second base film are each independently selected from at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohols and their derivatives, polytetrafluoroethylene and their derivatives, polyvinyl fluoride and their derivatives, polyvinylidene fluoride and their derivatives, and polyethylene terephthalate and its derivatives.

[0026] The second aspect of the present application provides a method for preparing the diaphragm, which includes: setting a slurry layer for forming an intermediate layer on a surface of a first base film, wherein the slurry layer includes the ceramic particles, polymer particles and a solvent; setting a second base film opposite to the slurry layer, and preparing the diaphragm after drying.

[0027] In any embodiment, the slurry layer is disposed on the surface of the first base film by transfer coating, spin spray coating, dip coating, or the like.

[0028] In any embodiment, the slurry layer further includes one or a combination of two or more of a binder, a dispersant, and a wetting agent.

[0029] In a third aspect of the present application, a secondary battery is provided, which includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator located between the positive electrode sheet and the negative electrode sheet; the separator is the separator described in the first aspect of the present application.

[0030] In any embodiment, the secondary battery is a lithium ion battery or a sodium ion battery.

[0031] In any embodiment, the secondary battery includes at least one of a battery cell, a battery module, or a battery pack.

[0032] According to a fourth aspect of the present application, there is provided an electrical device comprising the secondary battery according to the third aspect of the present application.

[0033] Compared with the prior art, the beneficial effects of the technical solution of this application include:

[0034] The present application forms a composite diaphragm with a sandwich structure by placing an intermediate layer including ceramic particles and polymer particles between two diaphragms, thereby effectively avoiding the problem of ceramic particles and polymer particles being easily detached. In addition, the diaphragm provided by the present application also has good mechanical strength and can be closed under overheating conditions, significantly reducing the probability of thermal runaway under abnormally high temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Also, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0036] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0037] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown;

[0038] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0039] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0040] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of the present application is shown;

[0041] Figure 6 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source;

[0042] Description of reference numerals:

[0043] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 lithium-ion battery; 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0044] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0045] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0046] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0047] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0048] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, it is mentioned that the method may also include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0049] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0050] As an important component of secondary batteries, the diaphragm plays the role of isolating the positive and negative electrodes of the battery. When a secondary battery has a short circuit or other abnormalities, the voltage and internal temperature rise sharply, which can easily cause the diaphragm to melt and break, and then thermal runaway may occur. In the prior art, ceramic coatings are often provided on the surface of the diaphragm to improve the thermal stability and mechanical strength of the diaphragm. However, there are still defects such as easy detachment of the ceramic layer and insufficient safety performance at abnormally high temperatures.

[0051] The present application forms a composite diaphragm with a sandwich structure by placing an intermediate layer including ceramic particles and polymer particles between two diaphragms, thereby effectively avoiding the problem of ceramic particles and polymer particles being easily detached. In addition, the diaphragm provided by the present application also has good mechanical strength, and can achieve closed pores under overheating conditions due to the melting of the polymer into a non-porous membrane-like material, significantly reducing the probability of thermal runaway under abnormally high temperature conditions.

[0052] The technical solutions described in the embodiments of the present application are applicable to a diaphragm, and are also applicable to a method for preparing a diaphragm, a secondary battery using the diaphragm, a battery module using a secondary battery, a battery pack using a secondary battery or a battery module, and an electrical device using at least one of a secondary battery, a battery module and a battery pack.

[0053] Diaphragm

[0054] A first aspect of the present application provides a diaphragm, which includes a first base film, a second base film and an intermediate layer; the intermediate layer is arranged between the first base film and the second base film; the intermediate layer includes ceramic particles and polymer particles.

[0055] On the one hand, since the thickness of the electrode sheet changes during the charge and discharge process of the battery, if the functional coating is disposed on the surface of the diaphragm base film facing the electrode sheet, it is very easy to cause the electrode sheet to be detached from the coating on the diaphragm surface. In the present application, the intermediate layer containing ceramic particles and polymer particles is disposed between the first base film and the second base film, which can effectively prevent the ceramic particles and polymer particles from falling off.

[0056] On the other hand, the present application uses granular polymer as a functional material for high-temperature closed-cell, which has a greater bulk density than fibrous polymer materials, thus having better high-temperature closed-cell function, and also has the advantages of easy thickness adjustment and excellent manufacturability. Ceramic particles help to enhance the heat resistance and puncture strength of the diaphragm.

[0057] In some embodiments, the porosity of the first base film is greater than the porosity of the second base film.

[0058] The diaphragm of the present application includes two layers of base membranes. If the two layers of base membranes have the same porosity, when they are superimposed, the fibers of one layer of base membrane are likely to block the pores of the other layer of membrane. However, when the two layers of base membranes have different porosities, the above-mentioned blockage is not likely to occur, which is conducive to making the diaphragm have good air permeability. The combination of base membranes with different porosities also helps to enhance the overall mechanical properties of the diaphragm.

[0059] Herein, porosity refers to the percentage of the pore volume in the base film to the total volume of the base film, which can be obtained, for example, by the following test method known in the art, such as using a mercury porosimeter and referring to GB / T 21650.1-2008 for testing.

[0060] In some embodiments, the ratio of the porosity of the first base film to the porosity of the second base film is greater than or equal to 1.02; for example, it can be about 1.02, 1.05, 1.1, 1.12, 1.15, 1.2, 1.22, 1.25, 1.27, 1.3, 1.5, 1.7, 2, 2.3, 2.5, 2.8, 3, etc.

[0061] When there is a slight difference in the porosity of the first base film and the second base film, for example, when the ratio between the two is greater than 1.02, it can have a certain good technical effect in improving the overall air permeability of the diaphragm.

[0062] In some embodiments, the ratio of the porosity of the first base film to the porosity of the second base film is 1.05 to 2.5.

[0063] According to test results, when the porosity ratio of the first base film to the second base film is 1.05 to 2.5, it is more conducive to improving the overall performance including air permeability and mechanical strength.

[0064] In some embodiments, the porosity of the first base film is 30% to 80%; for example, it can be about 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc.

[0065] In some embodiments, the porosity of the second base film is 30% to 70%; for example, it may be about 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, etc.

[0066] In some embodiments, the pore size of the first basement membrane is the same as or different from the average pore size of the second basement membrane; the two are independently selected from 0.05 to 4 μm; for example, they can be selected from 0.05 μm, 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, etc.

[0067] The pore size of the separator has a direct impact on battery performance. For example, for lithium-ion batteries, if the pore size is too large, such as more than 4 μm, it is easy for the positive and negative electrodes to come into direct contact or the separator to be pierced by lithium dendrites, causing a short circuit. On the contrary, if the pore size is too small, such as less than 0.05 μm, it may inhibit the movement of electrolyte solution ions, thereby increasing the internal resistance of the battery.

[0068] In some embodiments, the ratio of the thickness of the first base film to the thickness of the second base film is greater than or equal to 1.02; for example, it can be about 1.02, 1.05, 1.1, 1.12, 1.15, 1.2, 1.22, 1.25, 1.27, 1.3, 1.5, 1.7, 2, 2.5, 3, 3.5, 4, 4.5, 5, etc.

[0069] When the porosity of the first base film is greater than that of the second base film, the thickness of the first base film is made greater than that of the second base film, so that the first base film with a relatively loose structure has a thicker thickness, which is beneficial to ensure that the diaphragm has good mechanical strength.

[0070] In some embodiments, a ratio of a thickness of the first base film to a thickness of the second base film is 1.2-5.

[0071] According to test results, when the thickness ratio of the first base film to the second base film is 1.2 to 5, it is more conducive to improving the overall performance including air permeability, mechanical strength, etc.

[0072] In some embodiments, the thickness of the first base film is 1 to 12 μm; for example, it can be about 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, etc.

[0073] In some embodiments, the thickness of the second base film is 1 to 12 μm; for example, it may be about 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, etc.

[0074] In some embodiments, the materials of the first base film and the second base film are each independently selected from at least one of polyolefins and their derivatives, halogenated polyolefins and their derivatives, polyethers and their derivatives, polyetheretherketones and their derivatives, polyesters and their derivatives, polyimides and their derivatives, polyvinyl alcohol and their derivatives, polytetrafluoroethylene and their derivatives, polyvinyl fluoride and their derivatives, polyvinylidene fluoride and their derivatives, and polyethylene terephthalate and its derivatives.

[0075] In some embodiments, the first base film and the second base film are made of different materials.

[0076] When the first base membrane and the second base membrane are made of different materials, the mechanical properties and physical properties of the two can complement each other due to the different materials, which is beneficial to optimize the overall performance of the diaphragm.

[0077] In some embodiments, in the intermediate layer, the mass ratio of ceramic particles to polymer particles is 1.5 to 4; for example, it can be about 1.5, 1.8, 2, 2.2, 2.5, 2.7, 3, 3.3, 3.5, 3.8, 4, etc.

[0078] The mass ratio of ceramic particles and polymer particles will affect the high-temperature resistance and high-temperature closed-cell performance of the diaphragm. If there are too few ceramic particles and too many polymer particles (for example, the mass ratio of ceramic particles to polymer particles is less than 1.5), the high-temperature resistance of the diaphragm may be insufficient, and the polymer particles may cause a certain blocking effect on the pores of the base membrane; if there are too few polymer particles (for example, the mass ratio of ceramic particles to polymer particles is less than 4), the high-temperature closed-cell function of the diaphragm may be negatively affected.

[0079] In some embodiments, the average particle size Dv50 of the ceramic particles is 0.01 to 1 μm; for example, it can be 0.01 μm, 0.02 μm, 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, etc.

[0080] If the average particle size of the ceramic particles is too large (for example, greater than 1 μm), it will affect the consistency of the diaphragm thickness and is not conducive to improving the battery energy density; if the average particle size of the ceramic particles is too small (for example, less than 0.01 μm), pore blockage will easily occur.

[0081] In some embodiments, the average particle size Dv50 of the polymer particles is 0.01 to 1 μm; for example, it can be 0.01 μm, 0.02 μm, 0.05 μm, 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, etc.

[0082] If the average particle size of the polymer particles is too large (for example, greater than 1 μm), the thickness consistency of the diaphragm will be affected; if the average particle size of the polymer particles is too small (for example, less than 0.01 μm), it will not be conducive to the efficient pore closing effect.

[0083] In some embodiments, the thickness of the intermediate layer is greater than or equal to 0.3 μm; for example, it can be about 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc.

[0084] The thickness of the middle layer is related to the heat resistance effect, so a thickness greater than 0.3 μm is required to ensure a relatively good high temperature resistance effect.

[0085] In some embodiments, the thickness of the intermediate layer is 0.5 to 5 μm.

[0086] When the thickness of the intermediate layer is 0.5 to 5 μm, better technical effects can be achieved in terms of heat resistance and air permeability of the separator. If the thickness is too thick (for example, greater than 5 μm), the air permeability of the separator may be affected, thereby increasing the internal resistance of the battery.

[0087] In some embodiments, the intermediate layer further includes a binder.

[0088] In some embodiments, the binder includes one or a combination of two or more of the following: can be selected from polyacrylate, acrylic acid, and carboxymethyl cellulose.

[0089] In some embodiments, the material of the ceramic particles includes one or a combination of two or more of the following: boehmite (γ-AlOOH), aluminum oxide (Al2O3), barium sulfate (BaSO4), magnesium oxide (MgO), magnesium hydroxide (Mg(OH)2), silicon dioxide (SiO2), tin dioxide (SnO2), titanium oxide (TiO2), calcium oxide (CaO), zinc oxide (ZnO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), nickel oxide (NiO), cerium oxide (CeO2), zirconium titanate (ZrTiO3), barium titanate (BaTiO3), and magnesium fluoride (MgF2).

[0090] In some embodiments, the melting point of the polymer particles is 200-260°C.

[0091] When the polymer particles have the above melting point, if the temperature of the battery rises to its melting point due to a short circuit or other reasons, the diaphragm provided in the present application can achieve a closed-cell function, thereby reducing the probability of combustion and explosion of the battery.

[0092] In some embodiments, the material of the polymer particles includes one or a combination of two or more of the following: polycaprolactam (nylon 6), polyhexamethylene adipamide (nylon 66), polyhexamethylene dodecanediamide (nylon 612), polydecanediamide (nylon 1010), polydecene formamide (nylon 11), polydiphenyl ether sulfone, and polynonyl urea.

[0093] Preparation method of diaphragm

[0094] The second aspect of the present application provides a method for preparing a diaphragm of any embodiment of the first aspect of the present application, comprising: disposing a slurry layer for forming an intermediate layer on a surface of a first base film, wherein the slurry layer comprises the ceramic particles, polymer particles and a solvent; disposing a second base film opposite to the slurry layer, and preparing the diaphragm after drying.

[0095] In some embodiments, the slurry layer further includes one or a combination of two or more of a binder, a dispersant, and a wetting agent.

[0096] In some embodiments, the slurry layer may further optionally include a binder, wherein the binder includes one or a combination of two or more selected from the following groups: polyvinylidene fluoride, styrene butadiene emulsion, polybutyl acrylate, polyacrylic acid, polyisooctyl acrylate, methyl cyanoacrylate, polymethyl methacrylate, ethylene glycol dimethacrylate, polyacrylamide, and epoxy resin.

[0097] In some embodiments, the slurry layer may further optionally include a dispersant, and the dispersant may include one or a combination of two or more selected from the following groups: sodium polyacrylate, sodium polymethacrylate, sodium polymethylbenzene acrylate, sodium polymethylbenzene sulfonate, vinyl-modified polyether polyol, polycarboxylic acid styrene maleic anhydride copolymer, sodium methacrylate maleate copolymer, ammonium acrylate, citrate, sodium hexametaphosphate, sodium tripolyphosphate, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and polyvinyl alcohol.

[0098] In some embodiments, the slurry layer may further include a wetting agent, and the dispersant may include one or a combination of two or more selected from the following group: sodium dodecylbenzenesulfonate, water-soluble azone, sodium butylnaphthalenesulfonate, and nonylphenol polyoxyethylene ether.

[0099] In some embodiments, the slurry layer is disposed on the surface of the first base film by transfer coating, spin spray coating, dip coating, or the like.

[0100] In some embodiments, the method for preparing the diaphragm comprises:

[0101] S1. Dispersing ceramic particles and polymer particles in deionized water, and further adding one or a combination of two or more of a binder, a dispersant, and a wetting agent, and stirring well to obtain a slurry;

[0102] S2. Apply the slurry to one surface of the first base film by transfer coating, rotary spraying, dipping, etc., and attach the second base film to the surface of the slurry layer on the first base film by a composite roller before the slurry layer is completely dried, and obtain the diaphragm after drying.

[0103] Secondary battery

[0104] A third aspect of the present application provides a secondary battery, which includes the separator of any embodiment of the first aspect of the present application.

[0105] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charge and discharge process of the battery, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0106] In some embodiments, the secondary battery is a lithium ion battery or a sodium ion battery.

[0107] [Positive electrode]

[0108] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector. As an example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0109] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0110] In some embodiments, the positive electrode film layer includes a positive electrode active material. When the positive electrode plate is used in a lithium-ion battery, the positive electrode active material may be a positive electrode active material for a lithium-ion battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O2) and its modified compounds, etc. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0111] In some embodiments, when the positive electrode plate is used for a sodium ion battery, the positive electrode active material may be a positive electrode active material for a sodium ion battery known in the art. As an example, the positive electrode active material may be used alone or in combination of two or more. Among them, the positive electrode active material may be selected from sodium iron composite oxide (NaFeO2), sodium cobalt composite oxide (NaCoO2), sodium chromium composite oxide (NaCrO2), sodium manganese composite oxide (NaMnO2), sodium nickel composite oxide (NaNiO2), sodium nickel titanium composite oxide (NaNi 1 / 2 Ti 1 / 2 O2), sodium nickel manganese composite oxide (NaNi 1 / 2 Mn 1 / 2 O2), sodium iron manganese composite oxide (Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2), sodium nickel cobalt manganese composite oxide (NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), sodium iron phosphate (NaFePO4), sodium manganese phosphate (NaMn P O4), sodium cobalt phosphate compounds (NaCoPO4), Prussian blue materials, polyanion materials (phosphates, fluorophosphates, pyrophosphates, sulfates), etc., but the present application is not limited to these materials. The present application can also use other traditionally known materials that can be used as positive electrode active materials for sodium ion batteries.

[0112] In some embodiments, the positive electrode film layer may also optionally include a binder. For example, the binder may include one or a combination of two or more selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0113] In some embodiments, the positive electrode film layer may further include a conductive agent. For example, the conductive agent may include one or a combination of two or more selected from the group consisting of Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0114] In some embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode film layer, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the composite current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0115] [Negative electrode]

[0116] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. As an example, the negative electrode current collector has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0117] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0118] In some embodiments, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material can be a negative electrode active material for a battery known in the art. For example, the negative electrode active material includes one or a combination of two or more selected from the following group: natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, TiO2-Li4Ti5O 12 , Li-Al alloy. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for lithium-ion batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0119] In some embodiments, the negative electrode film layer may further include a binder. For example, the binder may include one or a combination of two or more selected from the group consisting of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0120] In some embodiments, the negative electrode film layer may further include a conductive agent. For example, the conductive agent may include one or a combination of two or more selected from the following group: Super P, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0121] In some embodiments, the negative electrode film layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0122] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode film layer, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0123] [Electrolytes]

[0124] The electrolyte plays the role of conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be selected from at least one of a solid electrolyte and a liquid electrolyte (i.e., an electrolyte).

[0125] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0126] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0127] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0128] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0129] [Diaphragm]

[0130] The separator of any embodiment of the first aspect of the present application is used as a separator of a secondary battery.

[0131] [Preparation of Secondary Battery]

[0132] The positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly through a winding process or a lamination process, and then the electrolyte is injected after being packaged in an outer package to prepare a secondary battery.

[0133] The outer packaging may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0134] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square or any other shape. Figure 1 The secondary battery 5 is a square structure as an example.

[0135] In some embodiments, reference Figure 2 , the outer packaging may include a shell 51 and a cover plate 53. Among them, the shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the diaphragm can form an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the lithium-ion battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0136] Battery modules, battery packs

[0137] In some embodiments, secondary batteries may be assembled into a battery module. The number of secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0138] Figure 3 4 is an example of a battery module. Figure 3 In the battery module 4, the plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of secondary batteries 5 may be fixed by fasteners.

[0139] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0140] In some embodiments, the secondary batteries may also be assembled into a battery pack.

[0141] In some embodiments, the battery modules 4 may also be assembled into a battery pack. The number of battery modules contained in the battery pack may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

[0142] Figure 4 and Figure 51 is a battery pack 1 as an example. Figure 4 and Figure 5 The battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0143] Electrical devices

[0144] The present application also provides an electric device, which includes a secondary battery provided in the present application. In some embodiments, the electric device includes at least one of the battery modules or battery packs provided in the present application. The secondary battery, battery module, or battery pack can be used as a power source for the electric device, and can also be used as an energy storage unit for the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited to these.

[0145] As the electrical device, a secondary battery, a battery module or a battery pack may be selected according to its usage requirements.

[0146] Figure 6 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the secondary battery, a battery pack or a battery module can be used.

[0147] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0148] Example 1

[0149] The separator and the lithium-ion battery cell including the separator are prepared according to the following steps:

[0150] 1. Diaphragm

[0151] (1) Providing a first base film and a second base film, wherein the first base film is made of polypropylene (PP), has a thickness of 6 μm, a porosity of 45%, and an average pore size of 0.4 μm; and the second base film is made of polyethylene (PW), has a thickness of 5 μm, a porosity of 38%, and an average pore size of 0.2 μm.

[0152] (2) Prepare a slurry for forming an intermediate layer. Alumina particles (average particle size Dv50: 0.1 μm) and polycaprolactam particles (average particle size Dv50: 0.1 μm) are mixed in a mass ratio of 8:2 to serve as a functional particle material; the functional particle material, polymethyl methacrylate used as a binder, and sodium carboxymethyl cellulose used as a dispersant are then dispersed in deionized water in a mass ratio of 9:0.5:0.5, and the mixture is stirred thoroughly to obtain a slurry. The functional particle material accounts for 5% by volume of the slurry.

[0153] (3) The slurry prepared in step (2) is applied to one surface of the first base film by transfer coating to form a slurry layer on the first base film; before the slurry layer is completely dried, the second base film is attached to the surface of the slurry layer on the first base film by a composite roller, and after drying, a separator I-1 is obtained. In the separator I-1, the thickness of the intermediate layer is 2 μm.

[0154] The separator I-1 was used to prepare a lithium-ion battery cell II-1.

[0155] 2. Lithium-ion battery cells

[0156] (1) Preparation of positive electrode sheet

[0157] LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, superconductive carbon black SP as a conductive agent and polyvinylidene fluoride (PVDF) as a binder are dispersed in N-methylpyrrolidone (NMP) as a solvent in a mass ratio of 96:2:2 and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and after drying, cold pressing, slitting and cutting, a positive electrode sheet is obtained.

[0158] (2) Preparation of negative electrode sheet

[0159] The negative electrode active material graphite, superconductive carbon black SP as a conductive agent, SBR as a binder and CMC-Na as a thickener are dispersed in deionized water as a solvent in a mass ratio of 96:1:1:2 and mixed evenly to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil; after drying, cold pressing, slitting and cutting, a negative electrode sheet is obtained.

[0160] (3) Diaphragm

[0161] The separator I-1 was prepared by the above steps.

[0162] (4) Preparation of electrolyte

[0163] Ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) are mixed evenly in a volume ratio of 1:1:1 to obtain an organic solvent, and then fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0164] (6) Preparation of battery cells

[0165] The positive electrode sheet, separator and negative electrode sheet are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare battery cell, the pole ears are welded, and the bare battery cell is placed in an outer package; the electrolyte is injected into the dried battery cell, and after packaging, standing, forming and shaping, a lithium-ion battery II-1 is prepared.

[0166] Example 2

[0167] The same steps as in Example 1 were followed to prepare a separator I-2 and a lithium ion battery II-2 comprising the same, except for the following differences:

[0168] The porosity of the first base film and the second base film are both 60%.

[0169] Example 3

[0170] The same steps as in Example 1 were used to prepare a separator I-3 and a lithium ion battery II-3 comprising the same, except for the following differences:

[0171] The porosity of the first base film and the second base film are both 35%.

[0172] Example 4

[0173] The same steps as in Example 1 were used to prepare a separator I-4 and a lithium ion battery II-4 containing the same, except for the following differences:

[0174] The thickness of the first base film and the second base film are the same, which is 6 μm.

[0175] Example 5

[0176] The same steps as in Example 1 were followed to prepare a separator I-5 and a lithium ion battery II-5 comprising the same, except for the following differences:

[0177] The alumina particles were replaced with boehmite particles (whose average particle size was the same as that of the alumina particles of Example 1).

[0178] Example 6

[0179] The same steps as in Example 1 were followed to prepare a separator I-6 and a lithium ion battery II-6 comprising the same, except for the following differences:

[0180] The polycaprolactam particles were replaced with polyhexamethylene dodecanediamide particles (whose average particle size was the same as that of the polycaprolactam particles in Example 1).

[0181] Example 7

[0182] The same steps as in Example 1 were followed to prepare a separator I-7 and a lithium ion battery II-7 comprising the same, except for the following differences:

[0183] The average particle size Dv50 of the alumina particles and the polycaprolactam particles was both 1 μm.

[0184] Example 8

[0185] The same steps as in Example 1 were followed to prepare a separator I-8 and a lithium ion battery II-8 comprising the same, except for the following differences:

[0186] The mass ratio of the alumina particles to the polycaprolactam particles is 3:2.

[0187] Example 9

[0188] The same steps as in Example 1 were used to prepare a separator I-9 and a lithium ion battery II-9 containing the same, except for the following differences:

[0189] The mass ratio of the alumina particles to the polycaprolactam particles is 9:1.

[0190] Example 10

[0191] The separator I-10 and the lithium ion battery II-10 comprising the same were prepared by the same steps as in Example 1 except for the following differences:

[0192] The mass ratio of the alumina particles to the polycaprolactam particles is 1:1.

[0193] Embodiment 11

[0194] The separator I-11 and the lithium ion battery II-11 containing the same were prepared by the same steps as in Example 1 except for the following differences:

[0195] The first base film had a thickness of 10 μm and a porosity of 43%.

[0196] Example 12

[0197] The separator I-12 and the lithium ion battery II-12 containing the same were prepared by the same steps as in Example 1 except for the following differences:

[0198] The first base film has a thickness of 12 μm and a porosity of 40%.

[0199] Example 13

[0200] The same steps as in Example 1 were used to prepare a separator I-13 and a lithium ion battery II-13 containing the same, except for the following differences:

[0201] In the separator I-13, the thickness of the intermediate layer was 0.5 μm.

[0202] Embodiment 14

[0203] The same steps as in Example 1 were followed to prepare a separator I-14 and a lithium ion battery II-14 comprising the same, except for the following differences:

[0204] In the separator I-14, the thickness of the intermediate layer was 5 μm.

[0205] Embodiment 15

[0206] The same steps as in Example 1 were used to prepare a separator I-15 and a lithium ion battery II-15 containing the same, except for the following differences:

[0207] The intermediate layer is formed by layering ceramic particles and polymer particles as follows:

[0208] Alumina particles and polycaprolactam particles are weighed respectively in a mass ratio of 8:2, and the alumina particles, polymethyl methacrylate used as a binder, and sodium carboxymethyl cellulose used as a dispersant are dispersed in deionized water in a mass ratio of 9:0.5:0.5, and stirred sufficiently to obtain a first slurry, wherein the mass volume percentage of the alumina particles in the first slurry is 35%; polycaprolactam particles, polymethyl methacrylate used as a binder, and sodium carboxymethyl cellulose used as a dispersant are dispersed in deionized water in a mass ratio of 9:0.5:0.5, and stirred sufficiently to obtain a second slurry, wherein the mass volume percentage of the polycaprolactam particles in the second slurry is 5%.

[0209] The first slurry is applied to one surface of the first base film by transfer coating to form a first slurry layer on the first base film; after the first slurry layer is dried, the second slurry is applied to the first slurry layer (the volume of the second slurry is the same as that of the first slurry) to form a second slurry layer; before the second slurry layer is completely dried, the second base film is attached to the surface of the second slurry layer by a composite roller, and after drying, a separator I-15 is obtained. In the separator I-15, the thickness of the intermediate layer is 2 μm.

[0210] Comparative Example 1

[0211] A single-layer base film is directly used, which is different from the first base film in Example 1 in that the porosity is 43%. A lithium-ion battery containing the single-layer base film is prepared according to the steps in Example 1.

[0212] Comparative Example 2

[0213] The separator and the lithium ion battery comprising the same were prepared by the same steps as in Example 1 except for the following differences:

[0214] The slurry used for preparing the intermediate layer does not include alumina particles and polycaprolactam particles.

[0215] That is, the diaphragm provided in this comparative example is obtained by compounding the first base film and the second base film, and does not contain ceramic particles and polymer particles.

[0216] Comparative Example 3

[0217] The separator and the lithium ion battery comprising the same were prepared by the same steps as in Example 1 except for the following differences:

[0218] The slurry used to prepare the intermediate layer does not include alumina particles.

[0219] Comparative Example 4

[0220] The separator and the lithium ion battery comprising the same were prepared by the same steps as in Example 1 except for the following differences:

[0221] The slurry used for preparing the intermediate layer does not include polycaprolactam particles.

[0222] Test Case

[0223] The following tests were performed on the separators and lithium-ion battery cells prepared in the above examples and comparative examples.

[0224] (1) Diaphragm air permeability

[0225] Take the diaphragms of the above embodiments and comparative examples, and test the air permeability according to the following steps: Cut 3 pieces of diaphragms 150 mm apart in the longitudinal direction on the film roll, and take a sample size of 100 mm × 100 mm. Place the diaphragm on a Japanese KRK Kumagai Wangken air permeability tester suitable for the test range for air permeability testing, and take the average of the 3 test results as the air permeability of the diaphragm. Then place the diaphragm on a glass plate, fix the four sides with paper clips, bake at 260°C for 1 hour, and test the air permeability again. A larger air permeability value represents worse air permeability, and a smaller air permeability value represents better air permeability.

[0226] (2) High temperature safety performance of batteries

[0227] The battery cells of the above-mentioned embodiments and comparative examples are placed in an oven at 260°C for 30 minutes. If the battery does not burn or explode, it means that the battery is not easy to burn or explode under high temperature conditions, and the probability of thermal runaway during use is low, which also reflects that the diaphragm used has good high-temperature closed-cell effect.

[0228] (3) Battery capacity retention rate

[0229] The capacity retention rate of the battery cells of each embodiment and comparative example was tested according to the following steps: at 25°C, the battery was charged to 4.55V at a constant current of 1C, then charged at a constant voltage of 4.55V until the current dropped to 0.05C, and then discharged to 2.5V at a constant current of 1C to obtain the first-week discharge capacity (Cd1); the charge and discharge were repeated for 100 cycles, and the discharge capacity of the lithium-ion battery after n cycles was obtained and recorded as (Cdn). Capacity retention rate = discharge capacity after n cycles / first-week discharge capacity.

[0230] (4) Puncture strength

[0231] The puncture strength of the diaphragms of the embodiments and comparative examples was tested according to the following steps: Referring to the national standard GB / T10004-2008, a test piece with a width of 100 mm was mounted on the sample membrane fixing clamp ring, and then a steel needle with a diameter of 1.0 mm and a top radius of 0.5 mm was used to puncture the test piece at a speed of (50±5) mm / min, and the load of the steel needle penetrating the test piece was read. The average value was taken after testing 5 points.

[0232] The test results are shown in Table 1.

[0233] Table 1 Test results of separator and battery cell

[0234]

[0235] Note: The diaphragms of Comparative Examples 1 to 4 shrank significantly after being baked at 260°C for 1 hour, so their air permeability values ​​after baking were not tested.

[0236] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A diaphragm, It is characterized in that The invention comprises a first base film, a second base film and an intermediate layer; the intermediate layer is arranged between the first base film and the second base film; the intermediate layer comprises ceramic particles and polymer particles.

2. The diaphragm according to claim 1, It is characterized in that The porosity of the first base film is greater than the porosity of the second base film.

3. The diaphragm according to claim 2, It is characterized in that The ratio of the porosity of the first base film to the porosity of the second base film is greater than or equal to 1.02; Optionally, the porosity of the first base film is 30% to 80%; Optionally, the porosity of the second base film is 30% to 70%.

4. The diaphragm according to any one of claims 1 to 3, It is characterized in that The thickness of the first base film is greater than the thickness of the second base film.

5. The diaphragm according to claim 4, It is characterized in that A ratio of a thickness of the first base film to a thickness of the second base film is greater than or equal to 1.02; Optionally, the thickness of the first base film is 1 to 12 μm; Optionally, the second base film has a thickness of 1 to 12 μm.

6. The diaphragm according to any one of claims 1 to 5, It is characterized in that The mass ratio of the ceramic particles to the polymer particles is 1.5-4.

7. The diaphragm according to any one of claims 1 to 5, It is characterized in that The average particle size Dv50 of the ceramic particles is 0.01 to 1 μm; Optionally, the average particle size Dv50 of the polymer particles is 0.01 to 1 μm.

8. The diaphragm according to any one of claims 1 to 7, It is characterized in that The material of the ceramic particles includes one or a combination of two or more of the following: boehmite, aluminum oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, cerium oxide, zirconium titanate, barium titanate, and magnesium fluoride.

9. The diaphragm according to any one of claims 1 to 7, It is characterized in that The material of the polymer particles includes one or a combination of two or more of the following: polycaprolactam, polyhexamethylene adipamide, polyhexamethylene dodecanoyl diamine, polydecanediamine, polydecylene sebacate, polydecylene formamide, polydiphenyl ether sulfone, and polynonylene urea.

10. The diaphragm according to any one of claims 1 to 9, It is characterized in that The thickness of the intermediate layer is greater than or equal to 0.3 μm; Optionally, the thickness of the intermediate layer is 0.5-5 μm.

11. A method for preparing the diaphragm according to any one of claims 1 to 10, It is characterized in that include: Disposing a slurry layer for forming an intermediate layer on one surface of the first base film, wherein the slurry layer includes the ceramic particles, polymer particles and a solvent; The second base film is arranged opposite to the slurry layer, and the diaphragm is prepared after drying.

12. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator between the positive electrode sheet and the negative electrode sheet, It is characterized in that The separator is the separator according to any one of claims 1 to 10.

13. An electrical device, It is characterized in that Includes the secondary battery as claimed in claim 12.

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